This patent application incorporates by reference subject matter contained in the U.S. patent application titled "Method and Apparatus for Determining a Need for Vehicle Braking System Maintenance," the latter application having U.S. Ser. No. 07/987,134, having common inventors and assignee, and being filed simultaneously herewith. The subject matter of the referenced patent application is incorporated for reference and is not essential to support the claims or to adequately disclose the invention of the present application.
Various systems for estimating the effectiveness of vehicle braking systems have been used. A common, "bookkeeping" method is to maintain records of the time elapsed and the number of miles travelled by a vehicle since its braking system has last been serviced so that such service can be performed before braking effectiveness declines to a critical level or to a level that incurs additional problems and/or expenses.
The bookkeeping method offers advantages of being uncomplicated and inexpensive. The conditions under which a vehicle may be driven during periods of similar duration, however, often vary between extremes, for example, heavy versus light traffic, hilly versus flat terrain, high versus low temperature and wet versus dry weather; and such extremes have a substantial affect on the rate and type of brake debilitation experienced. Consequently, the bookkeeping method cannot be expected to be consistently accurate, and disadvantages attending it include, at best, extra physical examinations and prematurely scheduled service and, at worst, service that is scheduled too late.
Brake lining wear does not always proceed at a linear rate, but it does require some time for wear to occur. Certain other parts of the braking system can, however, go from a fully functional condition to a nonfunctional condition very rapidly due to breakage or leakage resulting from the fatigue or injury of critical parts. If a nonfunctional part causes only a portion of the braking system to be nonfunctional or partly so, a driver might not notice the resulting decrease in braking efficiency for some time. During this period, additional damage is invited; and the linings of brakes remaining functional are likely to wear more rapidly than when all brakes are working with the same effectiveness.
While bookkeeping methods of determining the effectiveness of braking systems function with a certain degree of efficiency, they do not provide the advantages of the improved method and apparatus of the present invention as is hereinafter more fully described.